Method of inhibiting corrosion with amino diphosphonates

ABSTRACT

Amino diphosphonic acid compounds and water-soluble salts thereof alone and in combination with zinc are disclosed as inhibiting the corrosion of metals in contact with water.

United States Patent Hoover et al.

METHOD OF INHIBITING CORROSION WITH AMINO DIPHOSPHONATES Inventors:Merwin Frederick Hoover, Pittsburgh;

Gloria Di Marco Sinkovitz, Bridgeville; Andrew Martin Ruland,Pittsburgh, all of Assignee: Calgon Corporation, Pittsburgh, Pa.

Filed: Nov. 27, 1970 Appl. No: 93,419

us. c|.... ..252/181, 21 2Q7, 106/14,

Int. Cl. ..C02b 5/06, C231 1 1/16, C23f 14/07 Field of Search ..252/389,387, 8.55 E, 180,

[ June 6,1972

References Cited Primary Examiner-Leon D. Rosdol AssistantE.\'aminerlrwin Gluck V Attorney-William L. Kray er and Herbert .1v Zeh.Jr.

ABSTRACT Amino diphosphonic acid compounds and water-soluble saltsthereof alone and in combination with zinc are disclosed as inhibitingthe corrosion of metals in contact with water.

8 Claims, No Drawings METHOD OF INHIBITING CORROSION WITH AMINODIPHOSPHONATES BACKGROUND OF THE INVENTION This invention relates tocorrosion inhibiting in water systems, particularly industrial watersystems which utilize oxygen-bearing waters. More particularly, thisinvention relates to the use of amino diphosphonic acid compounds aloneand in combination with zinc as corrosion inhibitors.

Corrosion is a problem in almost every system where metal contactswater. This problem is very serious in most industrial water systemssince they contain large amounts of corrosive ingredients. The majorcorrosive ingredients found in these systems are dissolved gases such ascarbon dioxide and oxygen and inorganic salts such as the calcium,magnesium, and sodium salts of carbonate, bicarbonate, chloride andsulfate. These ingredients are especially corrosive to iron and steelwhich are extensively used in industrial water systems. However, copperand its alloys, aluminum and its alloys, and galvanized steel are alsoused in aqueous systems and are subject to the corrosive effects of theabove-mentioned ingredients. Therefore, it is necessary to treatindustrial water systems to prevent corrosion. Heretofore, the corrosioninhibitors in most. widespread use have contained either inorganicpolyphosphates or soluble chromates or combinations thereof. However,polyphosphates are hydrolytically unstable and have a tendency tohydrolyze and revert to the orthophosphate form which may formundesirable deposits. In addition, the toxic chromate containingcorrosion inhibitors present a waste disposal problem. Therefore, a newclass of corrosion inhibitors is desired.

SUMMARY OF THE INVENTION We have found that amino diphosphonic acidcompounds and water-soluble salts thereof alone, and especially, incombination with zinc are excellent corrosion inhibitors for industrialwater systems. The amino diphosphonic acid compounds of our inventionmay be represented by the following formula where R is an alkyl group ofone to five carbon atoms, phenyl, or benzyl and each M is independentlyselected from the group consisting of hydrogen, zinc, alkali metal, andammonium. The preferred compounds of our invention are when R is methylor phenyl and M is hydrogen and/or sodium. The compounds of ourinvention may be named as substituted lamino-methane-l,l-diphosphonicacid. For example, when R is phenyl, the compound is calledl-amino-l,phenyl methanel,l-diphosphonic acid amino benzyl diphosphonicacid) and when R is methyl, the compound is called l-aminol,methylmethane-l,l-diphosphonic acid (a amino ethane diphosphonic acid).

The amino phosphonic acid compounds of our invention are not novel. Forexample, see Blaser et al., U.S. Pat. No. 3,303,139, which is directedto the use of similar amino diphosphonates as metal complexing agents.See, also, U.S. Pat. Nos. 3,202,579; 3,317,340 and 3,446,582. However,heretofore these compounds have never been employed as corrosioninhibitors.

There are many different methods for preparing the applicable aminodiphosphonates as is known by one skilled in the art. Our invention isindependent of the method employed to synthesize the amino phosphonates.We have prepared the compounds of our invention by using three differentprocesses. The compounds were prepared by reacting an appropriateorganic nitrile with a phosphorous trihalide in the presence of aceticacid. Then, this intermediate was hydrolyzed with water to yield theamino diphosphonic acid. We have also prepared the compounds by reactingthe organic nitrile with an alcohol to form an imino ether. The iminoether was then reacted with a phosphite and hydrolyzed to yield theamino phosphonic acid. Finally, we have prepared the compounds of ourinvention by reacting an acid chloride with a phosphite and ammonia andhydrolyzing this reaction product to obtain the amino phosphonate.

Our amino diphosphonates will inhibit corrosion of metals whenmaintained in a water system at concentrations of at least about 20 ppm,preferably we desire to use about 50 ppm or more. The maximumconcentration will largely be determined by economic considerations.However, for all practical purposes, a concentration greater than 500ppm will never be used. As realized by one skilled in the art, theconcentration of amino diphosphonate needed to effectively inhibitcorrosion will ultimately depend on the characterization of the watersystem being treated and the particular amino diphosphonate being used.Therefore, the concentration ranges given herein are merely a generalindication of the amount of amino diphosphonate needed and the exactconcentration and particular compound will be determined by anexamination of the water system being treated.

While the amino phosphonates of our invention will inhibit corrosionwhen used alone, we have found that they are much more effective whenused in combination with zinc ion. The use of the amino diphosphonate incombination with zinc ions inhibits corrosion more effectively than theuse of the amino phosphonate alone or the zinc ions alone. Thiscombination of amino diphosphonate and zinc ions is a synergisticcombination. When using the zinc amino phosphonate combination, theamino diphosphonate is employed in concentrations ranging from 3 ppm toI00 ppm and the zinc ion is employed in concentrations ranging from 3ppm to I00 ppm. Preferably, the amino diphosphonate is used in aconcentration range of 5 to 50 ppm and the zinc ion is used in aconcentration range of 5 to 50 ppm. The ratio of zinc to organic aminodiphosphonate may vary from 1:10 to 1:1, preferably from 1:5 to l:2.5.The combination of amino diphosphonate and zinc will inhibit corrosionwhen used at concentrations of about 5 ppm, preferably we desire to useat least about 10 ppm. The upper limit is an economic consideration but,for all practical purposes, concentrations greater than lOO ppm willseldom, if ever, be needed.

When utilizing the combination of zinc ion and amino diphosphonate thereare many different ways of adding the zinc ion as is realized by oneskilled in the art. Our invention is independent of the method used tosupply the zinc ion so long as the zinc ion is present in theappropriate concentrations. The zinc ion may be added by utilizing awater-soluble zinc salt which forms zinc ions in solution. Some examplesofuseful water-soluble zinc salts are zinc chloride, zinc acetate, zincnitrate, and zinc sulfate. The zinc ion may also be supplied by addingzinc dust to an amino diphosphonic acid solution. The zinc dust reactswith the acid liberating hydrogen and forming a solution ofthe zinc saltof the amino diphosphonic acid. This method of adding the zinc ions ispreferred when extraneous ions would be somewhat deleterious to thesystem. However, we prefer to use zinc salts, particularly zinc sulfate,to supply the zinc ion. Zinc sulfate is commercially available,economical and only very slightly hygroscopic, yet readily soluble inwater.

The zinc ion and the amino diphosphonate may be added to the aqueoussystem separately or in combination. The easiest and preferred method isto add the compounds together. The amino diphosphonate and zinc salt maybe admixed to form a dry composition which can be added to the watersystem as a dry composition or dissolved and fed into the system as asolution. Such a dry admixture consists of from about 10 to 70 percentby weight zinc salt and from about 20 percent to about percent aminodiphosphonate. The exact composition of the admixture is chosen to givethe desired ratio of zinc to amino diphosphonate of from lzlO to l: l

We have performed numerous experiments which demonstrate theeffectiveness of our amino diphosphonates as corrosion inhibitors. Theseexperiments were performed by running a rotating coupon holder corrosiontest on the amino diphosphonates alone and in combination with zinc ion.In these experiments, number 1010AISI steel coupons were weighed andplaced in beakers containing about 1,000 milliliters of water at 140 Fand various amounts of the corrosion inhibitor compositions. The watercontained about 45 ppm bicarbonate, 75 ppm chloride, 320 ppm sulfate, 80ppm calcium, 25 ppm magnesium and had a total hardness as CaCO of about305 ppm and a pH of about 7.0. The coupons were rotated for 7 days. Thewater in the beakers was continuously being replaced at a rate of about1,000 milliliters per 12 hours. In addition, each beaker was equippedwith a gas dispersion tube which continuously bubbled air through thewater thereby keeping the water saturated with oxygen. After agitationfor seven days, the coupons were removed, cleaned and re-weighed. Theamount of corrosion that had taken place was determined by the loss inweight of the coupons and expressed in terms of milligrams of metalconsumed per square decimeter of surface area per day (mdd). The resultsare shown in the following tables.

TABLE 1 Inhibition of Corrosion of Steel with Zinc Ion and AlphaAminobenzyl Diphosphonic Acid Inhibitor Dosage in mg/l Corrosion RateInhibition of Corrosion of Steel with Zinc Ion and Alpha AminobenzylDiphosphonic Acid Inhibitor Dosage in mg/l Corrosion Rate ExampleDiphosphonate Zn in mdd 7 25 2.5 955 8 25 554 9 25 7.5 803 I0 25 8.3 668l l 25 10.0 12.! I2 25 12.5 13.3

TABLE 3 Inhibition of Corrosion of Steel with Zinc Ion and AlphaAminobenzyl Diphosphonic Acid Inhibitor Dosage in mg/l Corrosion RateExample Diphosphonate Zn in mdd I3 25 2.5 666 I4 25 5.0 t 11.1 25 7.5 96I6 25 8.3 8.7 [7 25 10.0 7.9 18 25 12.5 7.3

In Table 3 the initial water had twice the dosage listed but the feedwater contained the dosages listed in the table.

The data in the tables illustrate that the amino diphosphonates areeflective corrosion inhibitors, especially in combination with zinc ion.Moreover, the conditions of the test were quite severe, bein of an orderof magnitude of five times the severity normal y experienced in mostaqueous systems. Therefore, the amino diphosphonates of our inventionare quite effective corrosion inhibitors and may be used atconcentrations much lower than illustrated in the tables.

We claim:

1. A composition useful for inhibiting the corrosion of metals in anaqueous system consisting essentially of a source of zinc ion and anamino diphosphonate of the formula where R is selected from the groupconsisting of alkyl groups of one to five carbon atoms, phenyl andbenzyl and each M is independently selected from the group consisting ofhydrogen, alkali metal, ammonium and zinc and wherein the compositionhas a weight ratio of zinc ions to amino diphosphonate of from 1:10to1:1.

2. Composition of claim 1 wherein the source of zinc ion is awater-soluble zinc salt.

3. Composition of claim 1 wherein R is phenyl.

4. Composition of claim 1 wherein R is phenyl, M is selected fromhydrogen and sodium, and the source of zinc ion is zinc sulfate.

5. Method of inhibiting the corrosion of metals in a water systemcomprising maintaining in the water of said system at least 20 ppm of anamino diphosphonate of the formula where R is selected from the groupconsisting of alkyl groups of one to five carbon atoms, phenyl andbenzyl and where each M is independently selected from the groupconsisting of hydrogen, alkali metal and ammonium.

6. Method of claim 5 where R is phenyl and M is selected from hydrogenand sodium.

7. Method of inhibiting the corrosion of metals in a water systemcomprising maintaining in the water of said system about 3 to ppm ofzinc ion and about 3 to 100 ppm of an amino diphosphonate of the formulawhere R is selected from the group consisting of alkyl groups of one tofive carbon atoms, phenyl, and benzyl and where each M is independentlyselected from the group consisting of hydrogen, alkali metal, zinc andammonium.

8. Method of claim 7 where the source of zinc ion is zinc sulfate, R isphenyl, and M is selected from hydrogen and sodium.

2. Composition of claim 1 wherein the source of zinc ion is awater-soluble zinc salt.
 3. Composition of claim 1 wherein R is phenyl.4. Composition of claim 1 wherein R is phenyl, M is selected fromhydrogen and sodium, and the source of zinc ion is zinc sulfate. 5.Method of inhibiting the corrosion of metals in a water systemcomprising maintaining in the water of said system at least 20 ppm of anamino diphosphonate of the formula where R is selected from the groupconsisting of alkyl groups of one to five carbon atoms, phenyl andbenzyl and where each M is independently selected from the groupconsisting of hydrogen, alkali metal and ammonium.
 6. Method of claim 5where R is phenyl and M is selected from hydrogen and sodium.
 7. Methodof inhibiting the corrosion of metals in a water system comprisingmaintaining in the water of said system about 3 to 100 ppm of zinc ionand about 3 to 100 ppm of an amino diphosphonate of the formula where Ris selected from the group consisting of alkyl groups of one to fivecarbon atoms, phenyl, and benzyl and where each M is independentlyselected from the group consisting of hydrogen, alkali metal, zinc andammonium.
 8. Method of claim 7 where the source of zinc ion is zincsulfate, R is phenyl, and M is selected from hydrogen and sodium.